Friday, March 19, 2010

Understanding Your Body’s Anti-Starvation System

You’ve already learned how fat cells use lepti to talk to your brain, making it difficult to reduce your waistline without increasing your appetite. If that were the entire story, the science of food and dieting would be a tidy affair. Instead, the processes that regulate eating aren’t fully understood. They’re also multilayered, which means that your body uses multiple, redundant processes to get you to the dinner table. If something throws off the leptin signals, another system fills in to make sure you still feel hungry and get a good meal. This is one of the reasons that there’s no miracle pill for obesity on the way. When scientists attempt to tweak one set of hormones to promote light eating, the body adapts and chows down as steadily as ever.

Naturally Lean and Naturally FatThe discovery that different people harbor different numbers of fat cells hints at one of the unalterable truths about obesity. Some people struggle with weight their entire lives, while others wonder what all the fuss is about.

Truthfully, this shouldn’t come as a surprise. A long list of fascinating studies illuminates the strange workings of human fat storage. Here are some of the best:

• Starving the objectors. During World War II, more than a hundred men volunteered for a starvation study to avoid military service. Ancel Keys, a health researcher, took the 36 who were the most physically fit and psychologically healthy, cut their food intake to less than half, and put them on an intense walking regimen—similar to the punishing ordeals of the most hard-core dieter. The men lost a quarter of their weight over six months, and then were allowed to gain it back. During the dieting phase, they became obsessed with food, fantasizing about it for hours, collecting cooking implements, and scouring garbage cans. A few men broke the rules with sudden binging, after which they felt nauseated, depressed, and disgusted with themselves. And when they were allowed to choose their own meals again, many were no longer satisfied with normal portions, and ate insatiably. All of these details sound like a natural response to extreme circumstances—but they also have an uncanny similarity to the experiences of crash dieters.

• Feeding the prisoners. Another study took the opposite approach. Ethan Sims started with normal-weight volunteers from a state prison, and deliberately overfed and underexercised them until they grew fat. Much to everyone’s surprise, fattening people up was nearly as challenging as slimming them down. Different prisoners needed different amounts of excess calories to gain weight, but most of them required huge amounts of food to gain a significant amount of extra weight. At the end of the study, the prisoners effortlessly returned to their original weights—again at varying, self-determined rates.

• Comparing twins. It’s no surprise that people with obese parents are more likely to be obese themselves. There are a range of possible explanations, including poor dietary habits and bad role models. But more intriguing studies examine adopted children and identical twins who were raised in separate families. These studies found that fatness has a powerful genetic link—in other words, children are likely to drift toward the body mass of their birth parents, even if they’ve never met them.

Faced with this evidence, it’s natural to wonder what some people have done to deserve the short (and fat) end of the genetic stick. The oftenrepeated line that skinny people have fast metabolisms doesn’t seem to be true. Instead, people of all body weights maintain the same weight through most of their lives, eating an appropriate amount for their size. However, when people are pushed out of that range with forced starvation or overfeeding, the body fights back, making meaningful, long-term weight change extraordinarily difficult. This doesn’t mean that a fat person can’t get thin, but it certainly changes the rules of the game.

For popular accounts of fat research, check out these two slim books: The Hungry Gene (Ellen Ruppel Shell) explores the science and business of obesity research. Rethinking Thin (Gina Kolata) covers some of the same ground, while following a group of dieters in a weight-loss study who have big dreams but are destined to come up short.

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In its broadest sense, science (from the Latin scientia, meaning "knowledge") refers to any systematic knowledge or practice. In its more usual restricted sense, science refers to a system of acquiring knowledge based on scientific method, as well as to the organized body of knowledge gained through such research.

Fields of science are commonly classified along two major lines: natural sciences, which study natural phenomena (including biological life), and social sciences, which study human behavior and societies. These groupings are empirical sciences, which means the knowledge must be based on observable phenomena and capable of being experimented for its validity by other researchers working under the same conditions.